Environmental setting of human migrations in the circum-Pacific region

Aim To assess the genetic and archaeological evidence for the migration of modern humans out of Africa to the circum‐Pacific region and compare the migration patterns with Late Pleistocene and Holocene changes in sea level and climate. Location Southern and eastern Asia, Australia, and Oceania. Methods Review of the literature and detailed compilations of data on early human settlements, sea level, and climate change. Results The expansion of modern humans out of Africa, following a coastal route into southern Asia, was initially thwarted by a series of large and abrupt environmental changes. A period of relatively stable climate and sea level from c. 45,000 yr bp to 40,000 yr bp supported a rapid coastal expansion of modern humans throughout much of Southeast Asia, enabling them to reach the coasts of northeast Russia and Japan by 38,000–37,000 yr bp . Further northwards, migrations were delayed by cold northern climates, which began to deteriorate rapidly after 33,000 yr bp . Human migrations along the coast of the Bering Sea into the New World appear to have occurred much later, c. 14,000 yr bp , probably by people from central Asia who were better adapted to cold northern climates. Cold, dry climates and rapidly changing sea levels leading into and out of the Last Glacial Maximum inhibited coastal settlement, and many of the sites occupied prior to 33,000 yr bp were abandoned. After 16,000 yr bp , the sea‐level rise slowed enough to permit coastal ecosystems to develop and coasts to be re‐colonized, but abrupt changes in climate and sea level inhibited this development until after 12,000 yr bp . Between 12,000 yr bp and 7000 yr bp there was a dramatic increase in reef and estuary/lagoon ecosystems, concurrent with a major expansion of coastal settlements. This early Holocene increase in coastal environments and the concomitant expansion of human coastal‐resource exploitation were followed by corresponding declines in both phenomena in the mid‐Holocene, c. 6000–4000 yr bp . This decline in coastal resources is linked to the drop in sea level throughout the Pacific, which may have caused the widespread population dislocations that ultimately led to the human expansion throughout Oceania. Main conclusions Climate and sea‐level changes played a central role in the peopling of the circum‐Pacific region.     

Vegetation and fire history of a Chinese site in southern tropical Xishuangbanna derived from phytolith and charcoal records from Holocene sediments

Aim The aims of this paper are to reconstruct the vegetation and fire history over the past 2000 years in a well‐preserved rain‐forest area, to understand interactions between climate, fire, and vegetation, and to predict how rain forest responds to global warming and increased intensity of human activity. Location Xishuangbanna, south‐west China, 21–22° N, 101–102° E. Methods Phytolith (plant opal silica bodies) morphotypes, assemblages, and indices were used to reconstruct palaeovegetation and palaeoclimate changes in detail. Micro‐charcoal particles found in phytolith slides, together with burnt phytoliths and highly weathered bulliform cells, were employed to reconstruct a record of past fire occurrence. A survey of field sediments, lithology, and ¹⁴C dating were also employed. Results Phytoliths were divided into 11 groups and classified into 33 well‐described morphotypes according to their shape under light microscopy and their presumed anatomical origins and ecological significance. The phytolith assemblages were divided into six significant zones that reveal a complete history of vegetation changes corresponding to climate variation and fire occurrence. Phytolith assemblages and indices show that the palaeoclimate in the study area is characterized by the alternation of warm–wet and cool–dry conditions. Phytolith and charcoal records reveal that 12 fire episodes occurred. Comparison of burnt phytoliths with an aridity index (Iph) shows that fire episodes have a strong relationship with drought events. Main conclusions Our results indicate that fire occurrence in the tropical rain forest of Xishuangbanna is predominantly under the control of natural climate variability (drought events). Nearly every fire episode is coupled with a climatic event and has triggered vegetation composition changes marked by a pronounced expansion of grasses. This indicates that drought interacts with fire to exert a strong influence on the ecological dynamics of the rain forest. However, the impact of human activity in recent centuries is also significant. Our results are important for understanding the interactions between climate, fire, and vegetation, and for predicting how rain forest responds to global warming and increased human activity.     

Historical climate modelling predicts patterns of current biodiversity in the Brazilian Atlantic forest

Aim We aim to propose validated, spatially explicit hypotheses for the late Quaternary distribution of the Brazilian Atlantic forest, and thereby provide a framework for integrating analyses of species and genetic diversity in the region. Location The Atlantic forest, stretching along the Brazilian coast. Methods We model the spatial range of the forest under three climatic scenarios (current climate, 6000 and 21,000 years ago) with BIOCLIM and MAXENT. Historically stable areas or refugia are identified as the set of grid cells for which forest presence is inferred in all models and time projections. To validate inferred refugia, we test whether our models are matched by the current distribution of the forest and by fossil pollen data. We then investigate whether the location of inferred forest refugia is consistent with current patterns of species endemism and existing phylogeographical data. Results Forest models agree with pollen records and predict a large area of historical forest stability in the central corridor (Bahia), as well as a smaller refuge (Pernambuco) along the Brazilian coast, matching current centres of endemism in multiple taxa and mtDNA diversity patterns in a subset of the species examined. Less historical stability is predicted in coastal areas south of the Doce river, which agrees with most phylogeographical studies in that region. Yet some widely distributed taxa show high endemism in the southern Atlantic forest. This may be due to limitations of the modelling approach, differences in ecology and dispersal capability, historical processes not contemplated by the current study or inadequacy of the available test data sets. Main conclusions Palaeoclimatic models predict the presence of historical forest refugia in the Atlantic rain forest and suggest spatial variation in persistence of forests through the Pleistocene, predicting patterns of biodiversity in several local taxa. The results point to the need for further studies to document genetic and species endemism in the relatively poorly known and highly impacted areas of Atlantic rain forests of north‐eastern Brazil.     

Abrupt Changes in Bosmina (Cladocera,Crustacea) Assemblages During the History of the Ostrowite Lake (Northern Poland)

During the 10000-year history of the Ostrowite Lake, there have been several episodes of change in dominance amongst species of the genus Bosmina. The dominants were alternately B.longirostris and Eubosmina spp. Amongst the subgenus Eubosmina, two species prevailed in different periods:Bosmina coregoni and Bosmina reflexa. The first species, Bosmina coregoni, is characterized by long antennae and short carapace mucrones, while the second one, Bosmina reflexa, by short antennae and very long mucrones. Bosmina reflexa was dominant at the beginning of the lake's history (Preboreal, 10000--9000 BP) and during the early Subboreal Period (5000–3500 BP). Only a small number of remains of Bosmina longispina(Eubosmina spp.) were present along the entire profile. Such strong changes in the domination of Bosmina species were observed for the first time in the sediments of Polish lakes. A similar transition from one species to another has been described in a few German lakes and was linked to climate changes. However, the changes in the Ostrowite Lake do not correlate with climate changes, but most probably, with changes in the lake's trophic level. This is suggested by the simultaneous increase of Bosmina reflexa and a good indicator of eutrophy, Bosmina longirostris.     

The Pleistocene Ma U’Oi cave, northern Vietnam: palaeontology, sedimentology and palaeoenvironments

In November 2001, a Vietnamese-French team undertook the excavation of the Ma U’Oi cave in northern Vietnam. This limestone karst cave is located in the province of Hoà Binh, 70 km ESE from Hanoi and is typical of the northern Vietnam landscape. The site yielded an in situ mammalian fauna of a relatively modern composition. We also found a mixed fauna with a lower molar attributed to an archaic Homo(Demeter et al., in press). We estimate the age of Ma U’Oi fauna between 169 kyr, the age of Thum Wiman Nakin (Esposito et al., 1998) estimated by U/Th method and 80-60 kyr, the biochronological age of Lang Trang (Long et al., 1996), or even Holocene. The Ma U’Oi site is important because of the scarcity of Vietnamese sites of those particular levels. For that reason, it fills a gap in the biostratigraphy of Vietnam and permits new correlations with other sites of the mainland, especially those well documented from Thailand.     

Did Native Americans influence the northward migration of plants during the Holocene?

Abstract Long‐distance plant dispersal explains the rapid northward migration of plant species during the Holocene but the mechanisms by which it occurred are poorly understood. Given that Native Americans spread numerous cultigens over thousands of kilometres during the late Holocene, I examined historical literature for evidence of non‐cultigen dispersal or cultivation in North America's eastern woodlands. Cultivation references are included because a strong relationship between dispersal and indigenous flora husbandry is assumed. Sixty‐seven texts describing Native American lifestyle, cultural activities, and land management reported some form of plant use. Most accounts, however, focus on cultigen production or the use of indigenous flora for medicine or food without mention of dispersal. Twenty‐four of the texts described the trade, transport, or cultivation of plants indigenous to eastern North American woodlands. Most accounts focus on the informal production of food plants, especially trees and shrubs. Confounding these reports was clear evidence of observer bias, limited botanical knowledge, acculturation, and secrecy by Native American informants. Because of these shortcomings, the likelihood of widespread long‐distance plant dispersal by Native Americans could not be determined using historical literature. This activity was either not widespread or was not observed by, or revealed to, Europeans. To adequately test the Native American plant dispersal hypothesis, direct evidence from other sources (e.g. archaeobotancial data) will be required.     

The Sula Reef Complex, Norwegian shelf

Summary Cool-water carbonates in the aphotic zone of deep shelf and continental margin settings in the Northeast Atlantic are produced by the deep-water coral reefs withLophelia pertusa as the major framework builder. Through a compilation of side scan sonar, airgun and manned submersible surveys from several cruises to the mid-Norwegian Sula Reef Complex (SRC), the facies pattern and zonation of one of the largest deep-water reefs in the Northeast Atlantic is described in relation to the overall seabed topography. The late glacial to early postglacial iceberg scour on the crest and shoulder of the Sula Ridge provides settling ground for the scleractinian corals already in the early Holocene. Since then coral growth continues until today but was supposed to be disturbed by an environmental hazard, the so-called second Storegga event. The distinct distribution pattern of individualLophelia reefs on the Sula Ridge has stimulated a discussion on intrinsic environmental controls such as the bentho-pelagic coupling and the alternative hydrocarbon-based nutrition hypothesis.     

The origin of remnant forest stands of Pinus tabulaeformis in southeastern Inner Mongolia

Pinus tabulaeformis is an endemic species in northern China. The northern edge of its distribution corresponds to the northern margin of the monsoon climate. Several stands of Pinus tabulaeformis beyond its major range of distribution were found on the southeastern edge of the Inner Mongolia Plateau. Phytosociological analysis shows that the community structure, species composition and regeneration ability of Pinus trees in these stands are quite different from those within its continuous range of distribution. This paper presents palynological evidence to explain how and when these remnant communities were formed. Pinus tabulaeformis entered the study area in the mid-Holocene as the summer monsoon intensified, and declined when the summer monsoon weakened. Climatic change was the driving factor for the migration of Pinus tabulaeformis. It might be supposed that the competition between pine and oak forest during the mid-Holocene warm period also affected the immigration of pine. The remnant stands of Pinus tabulaeformis were apparently favored by the microhabitat of the sandy soils in valleys when the climate became drier. The remnant stands of Pinus tabulaeformis help stabilize the stand dunes. The protection of these stands is an important task of natural conservation in the study area.     

A high-resolution Late-Glacial – Holocene pollen diagram from Pian di Gembro (Central Alps, Northern Italy)

The local and regional history of vegetation and climate, from the Late Glacial to the present, is represented in a new, high-resolution pollen diagram from Pian di Gembro (1350 m asl), ten ¹⁴C dates providing a reliable time control. An open pioneer vegetation dominated by Artemisia, Gramineae, and and Chenopodiaceae followed the retreat of the glaciers after the Last Glacial Maximum. Shrub vegetation with Juniperus, Alnus viridis, and Salix expanded soon after. Denser Betula-Pinus forests were present in Pian di Gembro around 12,320 B.P. Their extent was greatly reduced by the climatic cooling of the Younger Dryas, when open vegetation spread again. The beginning of the Holocene was marked by a considerable expansion in mixed oak taxa. Corylus immigrated to the site at 9,250 B.P. Picea and Abies expanded at 7,370 B.P., recording an abrupt change in the structure of the vegetational belts. A coeval climatic change is evidenced in the GRIP records and also detectable through oscillations of the timberline. Signs of human impact are present since late Atlantic, becoming more intense around 2,200 B.P. As pasture lands increased, Abies and Fagus slowly disappeared. The introduction of Castanea and Juglans is dated to Roman times, and Secale to the Middle Ages. Received February 4, 2002 / Accepted August 2, 2002     

Multi-disciplinary evidence of the Holocene history of a cultivated floodplain area in the wetlands of northern Colombia

An environmental reconstruction of the last 10,000 ¹⁴C years of a frequently flooded wetland ecosystem in the lower Magdalena valley in northern Colombia is presented, on the basis of a multi-disciplinary study of the sediments of the upper 15 m of the core from Boquillas (74°33'E, 9°7'N; 20 m a. s. l.). We used the following studies: pollen, lithology, organic structures, clay mineralogy, soil and sediment geochemistry, and δ¹³C values. The chronology is based on 13 AMS radiocarbon dates; the humic acid fractions were used in the case of seven samples. Pollen from local origin (swamps, open grass-rich vegetation, and gallery forest) show the development of the wetland area. River-transported pollen from a greater distance (dry forest, montane forest, Alnus) show changes in river activity and reflect large-scale changes of climatic conditions in the Momposina basin. From c. 10,010 to 9370 uncal B. P. (zone BQS-Ia) the river system was of high energy, as inferred by the lithological changes. The landscape was dominated by open grass-rich vegetation with gallery forest along the streams. A marked representation of Alnus and montane forest taxa indicate significant water transport and river dynamics. Climatic conditions were dry. From c. 9370-8430 uncal B. P. (zone BQS-Ib) wetlands were isolated from the main river system, and clayey sediments with kaolinite, smectite and illite as the main minerals accumulated in a lower-energy environment. Climatic conditions were dry and changes in the seasonal precipitation favoured the expansion of the gallery forest. From c. 8430 to 8040 uncal B. P. (zone BQS-Ic) low values of river-transported pollen indicate dry climatic conditions and open vegetation became more abundant. The flooding frequency of the Boquillas site diminished. From 8040 to 4900 uncal B. P. (zone BQS-Id) the Boquillas site was dominated by open vegetation with patches of gallery forest along the streams. Supply of river-transported allochthonous pollen (from many sources) was minimal. Clay minerals from the sediments suggest variable temperature and precipitation. From c. 4900 to 1550 uncal B. P. )zone BQS-II) the site was within the reach of the main river system as is the case today. Frequent flooding, coinciding with peaks of river-transported grains of Alnus and high sediment supply, point to high precipitation in the composite catchment area of the Magdalena, Cauca, San Jorge, and Cesár rivers. High values of phosphorous in the upper part of the core point to the presence of a pre-Hispanic civilization, approximately from 2000 uncal B. P. onward. Construction of an extensive drainage system allowed irrigation as well as drainage depending the annual cycle of precipitation. The landscape was significantly modified and allowed an extensive crop production on a system of raised fields. Received May 18, 2001 / Accepted June 15, 2001